Water in Ionic Liquid Lubricants: Friend and Foe,ACS Nano

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Water in Ionic Liquid Lubricants: Friend and Foe
ACS Nano ( IF 15.8 ) Pub Date : 2017-06-26 00:00:00 , DOI: 10.1021/acsnano.7b01835
Oscar Y. Fajardo _{1,

2} , Fernando Bresme ₁ , Alexei A. Kornyshev ₁ , Michael Urbakh ₂

Affiliation

To a greater or lesser extent, most room-temperature ionic liquids (RTILs) absorb water from humid air. Penetration of water into the lubricating nanoscale film may affect its equilibrium structure and dynamic properties and thus influence the ability of RTILs as lubricants to reduce friction between solid surfaces. Here we investigate the impact of hydration on lubrication using nonequilibrium molecular dynamics simulations. Water adsorption changes both the ionic liquid molecules’ orientation and the slip conditions at the solid–liquid interfaces, resulting in a reduced resistance against squeezing-out of the lubricant by an external load. For the same normal load, the film becomes thinner when water is present. We show that even small amounts of water can screen the electrostatic interactions between the ions, making RTILs more “fluid” and compressible and hence less resistant to external stress. The impact that screening has on friction involves several aspects that are systematically analyzed in this paper.

中文翻译：

离子液体润滑剂中的水：敌意

大部分室温离子液体（RTIL）或多或少地从潮湿的空气中吸收水。水渗透到润滑性纳米级薄膜中可能会影响其平衡结构和动态特性，从而影响RTILs作为润滑剂减少固体表面之间摩擦的能力。在这里，我们使用非平衡分子动力学模拟研究水合对润滑的影响。水的吸附会改变离子液体分子的方向和固液界面处的滑移条件，从而降低了抵抗润滑剂在外部载荷下挤出的抵抗力。对于相同的法向载荷，当有水存在时，薄膜会变薄。我们证明，即使少量的水也可以屏蔽离子之间的静电相互作用，使RTIL更“流动”和可压缩，因此对外部压力的抵抗力降低。筛选对摩擦的影响涉及多个方面，本文对此进行了系统地分析。

更新日期：2017-06-28

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